My knowledge says, how you can do it:
1. Open a terminal on your OpsCenter server.
2. Navigate to the root user's home directory. This is typically `/root`. You can use the following command:
```bash
cd /root
```
3. Edit the `/etc/hosts` file using a text editor. You can use a command-line editor like `vi` or `nano`. For example:
```bash
nano /etc/hosts
```
4. Add an entry for your master server, including its IP address and hostname. For example:
```plaintext
192.168.1.2 mymasterserver
```
Replace `192.168.1.2` with the actual IP address of your master server, and `mymasterserver` with its hostname.
5. Save the changes and exit the text editor.
After making these changes, try adding the master server to OpsCenter again. If you continue to encounter the `opscenter-10939` error, consider checking the OpsCenter and NetBackup compatibility matrix to ensure that the versions are compatible. Additionally, verify network connectivity, firewall settings, and any security groups or policies that might affect communication between OpsCenter and the master server.
